1. Field of the Invention
The present invention relates to a photocoupling device which comprises an input section having a plurality of light emitting elements and lead terminals for supplying a drive current to these light emitting elements and an output section having a light receiving element opposed to light emitting faces of the light emitting elements and lead terminals for supplying a drive current to the light receiving element, and relates to a method of manufacturing the same.
2. Description of the Related Art
In recent years, it has become important to make equipment energy-saving. With regard to photocoupling devices, a photocoupling device of low input current driving type which can be directly driven by a microcomputer is expected to be mainstream as a photocoupling device from now. For example, in the case where it becomes possible to directly drive a photocoupling device by a microcomputer, the need for a transistor of a drive stage is eliminated. Especially, a plurality of photocoupling devices are needed in an interface section of FA (factory automation) equipment since a plurality of signals are inputted and outputted therein. Therefore, by using a low-input-driving photocoupler, effects of energy saving are increased. Moreover, it is also possible to downsize a current limiting resistor of a light emitting element, so that costs can be reduced.
Consequently, as equipment with a microcomputer becomes widespread, such equipment has been advanced, and a market of photocoupling devices has expanded. Therefore, a demand of developing a photocoupling device of low input current driving type which meets an energy-saving design has grown.
For example, in a microcomputer drive circuit such as a programming console, a conventional general-purpose photocoupling device (for example, a photocoupling device driven at a forward current IF (referred to as IF hereinafter) of 5 mA) is controlled by a microcomputer via a transistor of a drive stage. By using a photocoupling device of low input current driving type (for example, a photocoupling device driven at IF of 0.5 mA) instead of the general-purpose photocoupling device, the circuit can be directly driven by the microcomputer, the current can be reduced to one tenth, and the need of the transistor for the drive stage is eliminated. As a result, costs can be reduced.
In addition, in general household electrical appliances (for example, motor-controlled household electrical appliances such as an air conditioner, a microwave oven and a washer), a photocoupling device is used as an AC (alternating current) line zero cross point detecting device. The device is used for judgment whether frequency is 50 Hz or 60 Hz, detection of an instantaneous shutdown, detection of an AC zero cross point, timer count and so on. A current limiting resistor is inserted to directly drive a light emitting element of a photocoupling device with an AC power source. In this case, in a conventional general-purpose photocoupling device, a voltage of the AC power source is high when an input current is set to IF=5 mArms, so that a current limiting resistor of 20 kxcexa9/2W (which costs approximately 3 yen) is needed and power consumption reaches 500 mW. In the case where a photocoupling device of low input current driving type is used instead of the general-purpose photocoupling device, an input current can be limited to IF=0.5 mArms, so that it is enough to apply a current limiting resistor of 200 kxcexa9/0.25W (which is 1 yen or less), and power consumption is lowered to 50 mW. Accordingly, it is possible to achieve both cost reduction and energy saving.
As mentioned above, a variety of advantages can be obtained by making a photocoupling device drive at a low input current.
Next, a structure of a conventional photocoupling device of low input current driving type will be described referring to drawings.
FIG. 10 is a longitudinal sectional view showing an example of a conventional photocoupling device of low input current driving type, FIG. 11 is a transverse sectional view showing an example of the conventional photocoupling device of low input current driving type, and FIG. 12 is an explanatory view showing an example of a connection of the photocoupling device shown in FIGS. 10 and 11. Here, FIG. 11 mainly shows an input section.
The photocoupling device comprises an input section having a light emitting element 101 and an output section having a light receiving element 102 opposed to a light emitting face of the light emitting element 101.
The light emitting element 101 is die-bonded on a header 109a which is connected to one lead terminal 103a for the light emitting element, and further wire-bonded via a wire 105 on a header 109b which is connected to the other lead terminal 103b for the light emitting element. An exposed face of the light emitting element 101 is covered with a protecting resin layer 104 (shown in FIG. 10 only) which is formed by pre-coating with a transparent silicone resin.
On the other hand, the light receiving element 102 is die-bonded on a header 119a which is connected to one lead terminal 113a for the light receiving element, and further wire-bonded via a wire 115 on a header 119b which is connected to the other lead terminal 113b for the light receiving element.
Furthermore, the light emitting element 101 and the light receiving element 102 are covered with a first epoxy resin member 107 which is formed by primary molding with a light-transmitting epoxy resin, in a state where the light emitting face and the light receiving face are opposed to each other. This first epoxy resin member 107 is covered with a second epoxy resin member 106 which is formed by secondary molding with a light proof resin.
This photocoupling device has a 4-pin package (two pins on the input section side and two pins on the output section side).
In this example, a phototransistor is used as the light receiving element 102. As the light emitting element 101, a high-intensity light emitting element of GaAlAs or the like is used so as to drive with a low input current using a single light emitting element. By using the high-intensity light emitting element, not only the amount of light at a low current range is ensured but also sensitivity of the light receiving element is increased, thereby realizing a drive at a low input current. However, a high-intensity light emitting element of GaAlAs or the like is expensive, which costs at least three times more than a general-purpose light emitting element of GaAs or the like.
Next, a photocoupling device equipped with a plurality of elements will be explained referring to drawings.
FIG. 13 is a transverse sectional view showing another example of a structure of a conventional photocoupling device of low input current driving type. Here, FIG. 13 mainly shows an input section.
In general, as the number of elements increases, the number of headers 109c for mounting the elements and headers 109d for wire-bonding increases. In addition, along with the lead terminals 103a, 103b, 113a and 113b, lead terminals 103c, 103d, 113c and 113d are disposed. As compared with a 4-pin photocoupling device as shown in FIGS. 10 and 11, the above photocoupling device has a large package of 6-pin or 8-pin.
This photocoupling device is manufactured, in the same manner as a 4-pin photocoupling device as shown in FIGS. 10 and 11, through the steps of: mounting a light receiving element (not shown), a light emitting element 101 and another element 111 on specified headers 109a and 109c and connecting to lead terminals 103a, 103c and 113a; wire-bonding the light receiving element, the light emitting element 101 and the other element 111 on specified headers 109b, 109d and so on with wires 125a, 125b and so on and connecting to lead terminals 103b, 103d and 113b; and if necessary, pre-coating and so on. After that, lead frames on the input section side and on the output section sided are opposed to each other, and primary molding is performed in a state where the light emitting face of the light emitting element 101 is opposed to the light receiving face of the light receiving element. After this primary molding, burr removal and tie-bar cutting are done at the same time. Next, secondary molding is done, and burr removal and tie-bar cutting are done at the same time as well.
As mentioned above, although it is possible to design an input section of a photocoupling device with one light emitting element by using a high-intensity light emitting element for the purpose of realizing a photocoupling device of low input current driving type, a high-intensity light emitting element is quite expensive, which costs almost three times more than a general-purpose light emitting element.
In the case where a further reduction of drive current is demanded, it will be impossible to ensure sufficient brightness even when a high-intensity light emitting element is used. There is such a problem that it is difficult to increase brightness only by improving a light emitting element itself.
Further, in the case of disposing a plurality of headers inside a photocoupling device and simply increasing the number of light emitting elements, there is such a problem that the number of lead terminals also increases and a size of the package becomes large. Furthermore, although there may be such the case that an unused lead terminal is cut after packaging, this is merely for the purpose of creating an additional space between lead terminals (a lead space). In this case, too, it is impossible to utilize a dimension of a conventional general-purpose 4-pin photocoupling device, thereby creating a problem of making it difficult to design a downsized circuit board.
The invention is presented for the purpose of solving such problems as mentioned above. An object of the invention is to provide a photocoupling device which can supply sufficient light to a light receiving element by increasing the amount of light on an input section side with a low input current, and provide a method of manufacturing, with which such a photocoupling device can be assembled without adding an extra process.
The invention provides a photocoupling device comprising:
an input section having a plurality of light emitting elements and lead terminals for supplying a drive current to the light emitting elements; and
an output section having a light receiving element opposed to light emitting faces of the light emitting elements and lead terminals for supplying a drive current to the light receiving element,
wherein the plurality of light emitting elements are connected in series.
According to the invention, it is possible to cause a plurality of light emitting elements to emit light at a low input current, so that it is possible to achieve an increase of light amount and supply sufficient light to a light receiving element.
In the invention, it is preferable that the plurality of light emitting elements are connected in series via a plurality of headers.
According to the invention, it is possible to connect the plurality of light emitting elements in series only by wire-bonding the light emitting elements to headers adjacent thereto.
Further in the invention, it is preferable that at least one of the plurality of headers is provided with two light emitting elements.
Still further in the invention, it is preferable that structures of the two light emitting elements are different from each other.
According to the invention, it is possible to avoid increase of the number of the headers, so that it is possible to realize a further downsized photocoupling device.
Further in the invention, at least one of the plurality of headers may be a dummy header.
According to the invention, it is possible to downsize a package, so that it is possible to realize a further downsized photocoupling device.
Further in the invention, the dummy header may be lead-cut from a lead frame inside or outside a package which covers and protects the light emitting elements and the light receiving element.
According to the invention, especially in the case where the dummy header is lead-cut from a lead frame inside a package, it is possible to prevent a lead-cut portion of the header from protruding beyond the package, so that it is possible to increase an insulation performance between the input section and the output section.
The invention provides a method of manufacturing a photocoupling device comprising the steps of:
forming an input section having a plurality of light emitting elements and lead terminals for supplying a drive current to the light emitting elements and an output section having a light receiving element opposed to light emitting faces of the light emitting elements and lead terminals for supplying a drive current to the light receiving element;
connecting the plurality of light emitting elements in series via a plurality of headers, at least one of the plurality of headers being a dummy header; and
tie-bar cutting and lead cutting the dummy header at the same time.
According to the invention, it is possible to lead-cut a dummy header only by partly modifying the shape of a tie-bar cutting die, so that it is possible to assemble without adding an extra process.
Further in the invention, a lead-cut portion of the dummy header may be disposed in the vicinity of a tie-bar cut portion.
According to the invention, it is possible to minimize the need of modification of the shape of a tie-bar cutting die, and to reduce damages to a package during a cutting process.
The invention provides a method of manufacturing a photocoupling device, comprising the steps of:
forming an input section having a plurality of light emitting elements and lead terminals for supplying a drive current to the light emitting elements and an output section having a light receiving element opposed to light emitting faces of the light emitting elements and lead terminals for supplying a drive current to the light receiving element; and
connecting the plurality of light emitting elements in series via a plurality of headers, at least one of the plurality of headers being a dummy header,
wherein a lead frame is used in which the dummy header is connected to a header of another channel adjacent to the dummy header via a connecting member.
According to the invention, it is possible to lead-cut a dummy header only by partly modifying the shape of a tie-bar cutting die, so that it is possible to assemble without adding an extra process.